Different estimates of the seasonal effects in an economic time series can arise from different choices of the options in the seasonal adjustment software. Or, with an aggregate series, different estimates can also result from different choices of the level of aggregation at which seasonal adjustment is performed. One purpose of this paper is to illustrate some issues that arise in the seasonal adjustment of aggregate series. A second focus is to describe some useful ways of detecting adjustment inadequacies and assessing the quality of the adjustments.